Ball screw mechanism with improved ball guide

ABSTRACT

A ball screw mechanism includes a shaft with an external helical land and groove, and a nut which has an internal helical land and groove telescoped over the shaft. The nut rides on bearing balls located in a race defined by portions of the grooves of the nut and the shaft and the balls are recirculated continuously through the race as the nut turns relative to the shaft by means of a ball guide located in an opening through the side of the nut. A channel through the guide communicates between the ends of the race and passes over the land on the shaft to guide the balls from one end of the race to the other so the balls recirculate through the race. The balls hold the guide outwardly of the shaft and two projections extending laterally from opposite sides of the guide fit within the groove in the nut to keep the guide from being pushed through the opening while also holding the guide precisely in position so the opposite ends thereof deflect the balls into and out of the channel.

United States Patent [191 Eschenbacher et al.

[ BALL SCREW MECHANISM WITH IMPROVED BALL GUIDE [75] Inventors: RolfEschenbacher,

Nurtingen-Oberensingen; Hans-Gunter Steinbrenner, Wendlingen, both ofGermany [73] Assignee: Warner Electric Brake & Clutch Company, SouthBeloit, Ill.

[22] Filed: Nov. 24, 1972 [21] Appl. No.: 309,253

[52] US. Cl. 74/459 [51] Int. Cl. Fl6lt 55/22 [58] Field of Search74/459 [56] References Cited UNITED STATES PATENTS 3,234,8l0 2/1966Orner 74/459 3,669,460 6/1972 Wysong 74/459 x Primary Examiner-LeonardH. Gerin Attorney, Agent, or Firm-Wolfe, Hubbard, Leydig, Voit & OsannLtd.

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[ June 11, 1974 [5 7] ABSTRACT A ball screw mechanism includes a shaftwith an external helical land and groove, and a nut which has aninternal helical land and groove telescoped over the shaft. The nutrides on hearing balls located in a race defined by portions of thegrooves of the nut and the shaft and the balls are recirculatedcontinuously through the race as the nut turns relative to the shaft bymeans of a ball guide located in an opening through the side of the nut.A channel through the guide communicates between the ends of the raceand passes over the land on the shaft to guide the balls from one end ofthe race to the other so the balls recirculate through the race. Theballs hold the guide outwardly of the shaft and two projectionsextending laterally from opposite sides of the guide fit within the Vgroove in the nut to keep the guide from being pushed through theopening while also holding the guide precisely in position so theopposite ends thereof deflect the balls into and out of the channel.

BALL SCREW MECHANISM WITH IMPROVED BALL GUIDE BACKGROUND OF THEINVENTION The present invention relates to a ball screw mechanismincluding a shaft formed with an external helical land and groove and anut which is formed with an internal helical land and groove telescopedover the shaft and rides upon bearing balls confined within a racedefined by the grooves. More particularly, the invention relates to aball guide used in the mechanism to recirculate the balls through therace as the nut is moved relative to the shaft. The guide fits within anopening in the side of the nut and extends between the adjacent turns ofthe groove in the nut, and a channel through the guide communicatesbetween the turns so that the balls are guided over the land on theshaft as the nut turns relative thereto. Ball screw mechanisms of thetype described thus far are disclosed in Douglas U.S. Pat. No. 2,618,166and Goad U.S. Pat. No. 3,580,098.

SUMMARY OF THE INVENTION The general object of the present invention isto provide an improved ball screw mechanism which is easier and lessexpensive to manufacture and assemble than prior mechanisms of the samegeneral character. A furthe present invention is embodied in a ballscrew mechanism including a shaft 11 with a helical land 13 formed onthe exterior surface thereof and defining a helical groove 14 betweenthe turns of the land. A nut 15 telescoped over the shaft includes aland 16 and a groove 17 (see FIG. 2) both of which are formed on theinside surface of the nut, the groove 17 being approximately the samecross-sectional size and shape as the cross-sectional size and shape ofthe groove 14 and, similarly, the land 16 being about the samecrosssectional size and shape as the land 13.

The two grooves 14 and 17 are aligned with each other so that portionsof the grooves define a generally ring-shaped, hardened race 19 (FIG. 2)between the shaft 11 and the nut 15 and a plurality of bearing balls 20received within the race support the nut on the shaft. The depth of boththe grooves is about equal to one half the diameter of one of the ballsso that together the grooves define the race as having a diameterapproximately equal to the diameter of the balls. Be-

' cause of a slight clearance between the nut and the ther object is toaccomplish the foregoing by constructing the mechanisms in a uniquemanner whereby the ball guide and bearing balls may be assembled easilyand quickly with the nut and screw without need of ad ditional fasteningmeans such as screws or solder or the like.

A more detailed object is to take advantage of the groove of the nut toavoid having to perform a special cutting operation in the walls of thenut from the inside and at the same time use the balls to hold the guidein a precise position for recirculating the bearings through the race.

The invention also resides in the unique shape of the guide and in theuse of a projection which extends outwardly from the side of the guideto keep the latter from being pushed out of the opening by the ballswhile also coacting with the groove to hold the guide in a preciseposition to recirculate the balls.

These and other objects and advantages of the pres ent invention willbecome more apparent from the following detailed description when takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a ballscrew mechanism embodying the novel features of the present invention.

FIG. 2 is an elevational view of a part of the mechanism with partsbroken away and shown in cross section.

FIG. 3 is a fragmentary cross-sectional view taken substantially alongline 3-3 of FIG. 2.

FIG. 4 is a fragmentary cross-sectional view taken substantially alongline 4-4 of FIG. 2.

FIG. 5 is a fragmentary perspective view of parts of the mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in thedrawings for purposes of illustration,

shaft, the balls support the nut on the shaft for a relatively frictionfree transmission of force between the nut and shaft as the nut rotatesrelative to the shaft.

Herein, slightly less than one helical turn of the groove 17 in the nut15 defines the length of the race 19 and a ball guide 21 extendingbetween opposite ends of the race serves to recirculate the ballscontinuously through the race as the nut rotates in order to keep theballs from rolling out from between the nut and shaft 11. As shown inFIGS. 1, 2 and 4, the ball guide fits within an oval opening 23 throughthe side of the nut and includes a body 24 with a cross-sectional areavirtually the same shape as the shape of the opening so the guide canfit within the opening in only one way. The size of the area, however,is slightly smaller than the size of the opening to allow a slightclearance between the body and the side of the opening. A channel 25extending through the body communicates between the two ends of the raceby curving upwardly into the body to pass over the land 13 of the shaftso the balls may ride over the land when moving through the channelbetween the two ends of the race. As viewed in FIG. 2, the channel isslanted across the land 16 of the nut at an angle of about 45 withrespect to the helix angle of the land, and also the channel isgenerally S-shaped so the sides of the channel adjacent each end thereofprovide smooth transition surfaces 26 for deflecting the balls from therace and into the channel. Thus, with the guide of the presentarrangement secured within the opening 23, the balls may ride across thesurface of the land 13 and recirculate smoothly through the racenotwithstanding the direction of rotation of the nut relative to theshaft.

In accordance with the primary aspect of the present invention, aprojection 27 conforming generally to the size and to the shape of thegroove 17 of the nut 15 extends from the side of the guide 21 andcooperates with the balls 20 in a novel manner to hold the guide withinthe opening 23. For this purpose, the projection extends generally in alateral direction away from the side of the guide, beyond the edge ofthe opening and into the groove 17, and the balls hold the guideoutwardly from the shaft 11 seating the projection within the groove.This unique arrangement enables the ball screw mechanism 1% to beassembled without the need of special fastening means such as screws,solder or the like for holding the guide in position to recirculate theballs. Moreover, because of the size .and shape of the projection, thepresent invention takes advantage of the groove both to hold the guideprecisely in position and to avoid having to cut a recess in theinterior surface of the nut in order for the projection to be kept fromengaging the shaft.

In the present instance, two projections 27 extend outwardly from thebody, one projection being formed on each side of the body and extendingoutwardly therefrom at an angle of about 45 with respect to thelongitudinal axis of the body 24. Moreover, the projections are offsetlongitudinally from each other, one projection being located on one sideof the body adjacent one end of the channel 25 while the otherprojection is located on the opposite side of the body adjacent theother end of the channel. On both sides of the body, the projectionsextend away from the open ends of the channel and into portions 29 ofthe groove 17 beyond the race 19. In other words, the projections extendinto the groove of the nut adjacent each end of the race.

Advantageously, each projection 27 is shaped in conformity with thegroove 17 (see FIGS. 2, 3'and 4) as a longitudinally curved, generallycylindrical section having a semicircular cross-sectional areavirtuallythe same size and shape as the cross-sectional area of thegroove. In addition, each projection includes an outer end surface '30which extends generally parallel with the adjacent side of the body. Abottom surface 31 curved concentrically with the central axis of the nutdefines the thickness of each projection as being substantially equal tothe depth of the groove. Accordingly, when the guide is inserted in theopening 23, the bottom surfaces of the projections remain spacedslightly from the outer surface of the land 13 on the screw shaft 11;Moreover, with the two projections extending laterally beyond theedge ofthe opening and the balls holding the guide upwardly to seat theprojections in the grooves, the guide is held precisely in position toavoid an inaccurate alignment of the channel 25 with the race 19 therebyassuring a smooth flow of the balls 20 through the channel. Thus, withthis arrangement the guide is held within the nut without the need ofadditional fastening means'such as screws, solder or the like and, bytaking advantage of the groove 17 in the nut, it is unnecessary in themanufacture of the ball screw mechanism 10 to machine the interiorsurface of the nut to form recesses for receiving the'projections.

Assembly of the ball screw mechanism 10' also is simplified as a resultof the present invention and is accomplished by inserting the guide 21in the opening 23 from inside the nut 15. Then, use of a weakly adhesivegrease serves to hold the balls 20 in the race 19 and channel 25 topermit a cylindrical arbor (not shown) to be inserted into the nut. Thearbor holds the balls and guide in position and is pushed out of the nutas the shaft 11 carefully is telescoped into the nut and rotated toengage the bearing balls to complete the assembly of the mechanism. Whenthe assembly is completed, the guide is held precisely in position bythe projections on one hand and by the balls on the other hand.

To protect the interior of the assembled mechanism 10 against theinfiltration of dirt through the opening 23 and also to avoid the lossof grease. or lubricant through the opening, a sealing member 33 isprovided between the side of the opening and the guide 21. Herein, themember comprises an O-ring which is seated within a groove 34surrounding the body 24 of the guide adjacent the top of the body. Whenthe guide is inserted into the opening, the ring is squeezed between thebody and the side of the opening and thus prevents the infiltration ofdirt and loss of lubricant.

We claim as our invention:

1. In a ball screw mechanism, the combination of a shaft with anexternal helical land and groove, a nut with an internal helical landand groove and telescoped over said shaft, a plurality of bearing ballslocated in a race defined by portions of said grooves, and a ball guidelocated in an opening through the side of the nut and having a channelcommunicating between opposite ends of the race and over the land on theshaft to recirculate the balls through the race as the nut turnsrelative to the shaft, the improvement in said mechanism comprising, aprojection extending from one side of the guide, beyond the edge of theopening and into and along the groove in a generally circumferentialdirection relative to said groove from said opening, said balls holdingthe guide outwardly of the shaft to seat said projection within saidgroove in the nut whereby the guide is held in position with theopposite ends thereof precisely located in opposite ends of the race todeflect the balls into and out of the channel. r

2. In a ball screw mechanism, the combination of a shaft with anexternal helical land and groove, a nut with an internal helical landand groove and telescoped over said shaft, a plurality of bearing ballslocated in a race defined by portions of said grooves, and a ball guidelocated in an opening through the side of the nut and having a channelcommunicating between opposite ends of the race and over the land on theshaft to recirculate the balls through the race as the nut turnsrelative to the shaft, the improvement in said mechanism comprising twoprojections extending from opposite sides of the guide, beyond the edgeof the opening and into and along the groove in opposing generallycircumferential directions relative to said groove away from saidopening, said balls holding the guide outwardly of the shaft to seatsaid projections within said groove in the nut whereby the guide is-heldin position with the opposite ends thereof precisely located in oppositeends of the race to deflect the balls into and out of the channel.

3. A ball screw mechanism as defined by claim 2 wherein each of saidprojections is curved lengthwise to conform with the curvature of theinterior of said nut and each projection has a cross-sectional size andshape conforming to the size and shape of the crosssectional area of thegroove in the nut.

4. A ball screw mechanism as defined by claim 3 with a peripheral grooveformed in said guide around the sides thereof and including a sealingmember adapted to fit within said groove between the guide and the sidesof said opening.

1. In a ball screw mechanism, the combination of a shaft with anexternal helical land and groove, a nut With an internal helical landand groove and telescoped over said shaft, a plurality of bearing ballslocated in a race defined by portions of said grooves, and a ball guidelocated in an opening through the side of the nut and having a channelcommunicating between opposite ends of the race and over the land on theshaft to recirculate the balls through the race as the nut turnsrelative to the shaft, the improvement in said mechanism comprising, aprojection extending from one side of the guide, beyond the edge of theopening and into and along the groove in a generally circumferentialdirection relative to said groove from said opening, said balls holdingthe guide outwardly of the shaft to seat said projection within saidgroove in the nut whereby the guide is held in position with theopposite ends thereof precisely located in opposite ends of the race todeflect the balls into and out of the channel.
 2. In a ball screwmechanism, the combination of a shaft with an external helical land andgroove, a nut with an internal helical land and groove and telescopedover said shaft, a plurality of bearing balls located in a race definedby portions of said grooves, and a ball guide located in an openingthrough the side of the nut and having a channel communicating betweenopposite ends of the race and over the land on the shaft to recirculatethe balls through the race as the nut turns relative to the shaft, theimprovement in said mechanism comprising two projections extending fromopposite sides of the guide, beyond the edge of the opening and into andalong the groove in opposing generally circumferential directionsrelative to said groove away from said opening, said balls holding theguide outwardly of the shaft to seat said projections within said groovein the nut whereby the guide is held in position with the opposite endsthereof precisely located in opposite ends of the race to deflect theballs into and out of the channel.
 3. A ball screw mechanism as definedby claim 2 wherein each of said projections is curved lengthwise toconform with the curvature of the interior of said nut and eachprojection has a cross-sectional size and shape conforming to the sizeand shape of the cross-sectional area of the groove in the nut.
 4. Aball screw mechanism as defined by claim 3 with a peripheral grooveformed in said guide around the sides thereof and including a sealingmember adapted to fit within said groove between the guide and the sidesof said opening.